Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the engine, the heated coolant then circulated through a radiator to dissipate the heat. The cooling system may include various components such as a coolant reservoir coupled to the system for degassing and storing coolant. A pressurized reservoir that also serves to separate entrained air from the coolant is typically called a degas bottle. When the temperature of coolant anywhere in the system rises, thermal expansion of the coolant causes pressure to rise in the degas bottle as the trapped air volume reduces. Pressure relief can be achieved by releasing air from the degas bottle through a valve that is typically mounted in the fill cap. Then, when the temperature and pressure of coolant drops below atmospheric pressure in the degas bottle, air may be drawn back into the bottle through another valve that is often mounted in the fill cap.
If the coolant level in bottle is too low, the air volume will be too large to build sufficient pressure to prevent boiling and cavitation at the water pump inlet. At low fluid levels, the degas bottle will also no longer be able to separate air from the coolant and air can be drawn into the cooling system, again leading to poor cooling performance. If an overflow system is employed instead of an active degas system, a similar loss in cooling system performance can be realized when fluid levels are low.
Various approaches may be used to estimate fluid level in a reservoir. One example approach described by Murphy in U.S. Pat. No. 8,583,387 uses an ultrasonic fluid level sensor installed at the bottom of a reservoir to estimate a fluid level of the reservoir. However, the inventors herein have recognized that in such a cooling system, the dimensions of the coolant reservoir may vary based on the temperature of coolant contained in the reservoir. As a result, there may be inconsistencies in the estimated coolant level. Additionally, due to the location of the sensor at the bottom of the container, at low coolant levels, it may be unclear whether the fluid level in the reservoir is low or empty. Further still, it may be difficult to differentiate actual low coolant levels from incorrect coolant level estimation due to sensor degradation. In another example approach, described by Gordon et al in US 20130103284, the sensor is coupled to a coolant reservoir hose. One issue with such an approach is that the sensor can only detect the presence of coolant at that location in the circuit. Critical components of the power train may not be receiving coolant despite the presence of coolant in one of the coolant reservoir hoses, particularly if that hose is isolated from the cooling system by a valve (e.g., the engine thermostat hose). Further, while an indication of low coolant fluid level is received, engine temperature control may already be degraded due to substantial emptying of the coolant reservoir.
In one example, the above issues may be at least partly addressed by a method for a coolant system, comprising: estimating fluid level in a coolant reservoir based on a sensor coupled in a vertical standpipe aligned parallel to the reservoir, the standpipe fluidically coupled to the reservoir at each of a top and bottom location; and limiting engine power based on the estimated fluid level. In this way, changes in coolant level state based on transient changes in estimated coolant level may be reduced, and appropriate measures may be taken to avoid engine overheating when the coolant level state is empty versus low, or if the sensor has been faulted or degraded for longer than a threshold duration.
As one example, an engine coolant system may include a vertical tube aligned with a coolant overflow reservoir, the tube housing an ultrasonic sensor. The vertical tube may be coupled to the coolant reservoir at each of a top and bottom location via hoses, coolant flowing between the tube and the reservoir via the hoses. The hoses may be connected such that a headspace is generated between the top of the fluid level in the vertical tube and the top of the tube. In addition, the hoses may be connected such that the top of the vertical tube is arranged at a lower height than the top of the coolant reservoir, thereby allowing the sensor to more reliably estimate the fluid level in the reservoir and distinguish between low and empty coolant level states. The sensor, positioned inside a recess at the bottom of the vertical tube, may transmit a signal to the top of the vertical tube, an echo of the signal being received at the sensor after being reflected off the top of the tube. The signal may be transmitted periodically and based on an average echo time (which is the time elapsed between the signal being transmitted and an echo of the signal being received), the coolant level in the vertical tube may be estimated. This estimate may then be used to infer the coolant level in the reservoir. Changes in coolant level state may then be performed based on a change in coolant reservoir fluid level over a threshold duration. This allows the coolant level state to be updated only after the fluid level estimate has stabilized. Diagnostic codes may then be set based on the coolant level state. Further, engine power may be limited to different degrees based on the coolant level state. As an example, in response to an indication of low coolant level, a first diagnostic code may be set and engine load may be limited by a first amount to reduce engine overheating. In addition, fuel injection may be disabled for a duration to reduce the amount of heat transferred to the engine coolant. The first diagnostic code may be cleared upon completion of the key cycle. If a time elapsed since entering the first diagnostic mode exceeds a threshold duration, and the coolant state is still low, or has changed to EMPTY, a second diagnostic code may be set and engine power may be limited by a second, larger amount. For example, in the second diagnostic mode, the engine may be forced to operate at idle. In addition, the second diagnostic code may not be cleared until the vehicle is taken to a service technician and a dealer code has been entered.
In this way, an accuracy and reliability of determining a coolant level of a coolant overflow reservoir can be increased. By inferring the coolant level of the reservoir based on an estimated coolant level of a standpipe coupled to the reservoir, inaccuracies in coolant level estimation due to distortion of an in-tank sensor output during thermal fluctuations, or vehicle motion, is reduced. By updating the coolant level state of the coolant overflow reservoir selectively based on changes in coolant level at the standpipe of the over duration, frequent and erratic coolant level estimation can be reduced. In addition, unintentional triggering of an engine failure mode is reduced. As such, this reduces the frequency with which engine output is unnecessarily limited. By relying on an ultrasonic sensor and the local processor to estimate the coolant level of the standpipe based on an echo time, coolant level estimation can be expedited. Overall, engine overheating due to inaccurate coolant level estimation can be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.